Experimental investigation of a rotational MHD couette flow in a coplanar field

M. M. Gurfink

Abstract
The flow of an electrically conducting fluid between coaxial cylinders in a coplanar magnetic field is investigated by measuring the torque. The inner cylinder is rotated and the torque is determined from the angle of rotation of the outer cylinder, which is suspended from three wires. A circular magnetic field is produced by a dc current passing through a rectilinear cylindrical wire coaxial with the working cylinders. The experiments indicated that in the flow investigated, the magnetic field does not prevent the formation of the well-known Taylor eddy flow but delays it to higher Reynolds numbers, after which a turbulent flowoccurs. The experimental data on the transition is satisfactorily approximated by the linear dependence of the critical Reynolds number on the Stuart number, from which it follows that at large Reynolds numbers there is a critical value of the ratio between the Hartmann and Reynolds numbers (Ha/Re)_cr=const=0.015. Measurements under turbulent flow conditions provide quantitative data showing the influence of the magnetic field on the friction, and it is established that, as in a rectilinear tube in a longitudinal magnetic field, the Ha/Re ratio is a characteristic parameter which determines the index of the radical of the power dependence of the turbulent friction factor on the Reynolds number.